AP Physics 2 Questions: Right-Hand Rule for Force on a Wire

📚 Quick Study Guide

🧭
• Right-Hand Rule: Point your fingers in the direction of the current, curl them towards the magnetic field, and your thumb points in the direction of the force.
🧲
• Force on a Wire Formula: $F = ILB\sin(\theta)$, where $F$ is the force, $I$ is the current, $L$ is the length of the wire, $B$ is the magnetic field strength, and $\theta$ is the angle between the wire and the magnetic field.
📐
• Direction: The force is always perpendicular to both the current and the magnetic field.
⚡
• Maximum Force: Occurs when the current and magnetic field are perpendicular ($\theta = 90^\circ$), so $F = ILB$.
🚫
• Zero Force: Occurs when the current and magnetic field are parallel ($\theta = 0^\circ$) or anti-parallel ($\theta = 180^\circ$), so $F = 0$.

Practice Quiz

1. A wire carrying current is placed in a uniform magnetic field. The force on the wire is maximum when:
   1. The wire is parallel to the magnetic field.
   2. The wire is perpendicular to the magnetic field.
   3. The wire is at an angle of 45° to the magnetic field.
   4. There is no current in the wire.
2. A straight wire of length 0.2 m carries a current of 5 A. It is placed in a uniform magnetic field of 0.4 T. If the wire is perpendicular to the field, the force on the wire is:
   1. 0.2 N
   2. 0.4 N
   3. 0.8 N
   4. 1.0 N
3. If the direction of the current in a wire is reversed, the direction of the force on the wire in a magnetic field:
   1. Remains the same.
   2. Is reversed.
   3. Becomes zero.
   4. Increases in magnitude.
4. A wire carrying current runs from North to South. A magnetic field points East. The force on the wire is directed:
   1. East
   2. West
   3. Upward
   4. Downward
5. A wire is placed in a magnetic field such that the force on it is zero. This happens when:
   1. The current is very high.
   2. The magnetic field is very strong.
   3. The wire is parallel to the magnetic field.
   4. The wire is perpendicular to the magnetic field.
6. A wire carries a current of 2 A in a magnetic field of 0.5 T at an angle of 30 degrees. If the length of the wire within the field is 1 m, what is the force on the wire?
   1. 0.25 N
   2. 0.5 N
   3. 0.75 N
   4. 1.0 N
7. Two parallel wires carry current in the same direction. The force between them is:
   1. Attractive
   2. Repulsive
   3. Zero
   4. First attractive, then repulsive